This invention relates generally to electroplating apparatus and methodology, and more specifically, relates to apparatus useful in recovering from electrolytes metals, the ionic species of which are present at relatively low concentrations.
Particularly in the electroplating of precious metals, including especially gold, it has long been of interest to recover from the spent electroplating baths, the relatively low concentrations of gold remaining in same. The interest in such techniques, has of course, greatly intensified within recent years in view of the soaring price of gold. The same intense interest exists, with respect to recovery of other precious metals (e.g. silver), the market price for which have exhibited corresponding increases. It should also be pointed out that interest as well is evident in the recovery of metals which are not normally regarded as "precious," in view especially of increasing prices in these more common metals. Similarly, it should be appreciated that valuable metal species are often sought to be recovered from solutions that have not been used in electroplating--e.g., the silver in photographic baths, or metal species in manufacturing effluents. These solutions can in many instances also be treated by the present invention.
The prior technology applicable to the above field is well illustrated by the techniques presently utilized on a large scale in the gold plating industry. In such industry, the gold drag-out tank typically contains gold in ionic form, at concentrations of the order of 100 ppm or higher. Such electrode solutions are commonly treated with a suitable resin or other compositions; or various mechanical or electromechanical devices have been utilized to recover whatever gold can be gained in that manner.
Thereafter, a further rinse of the modified bath is effected with use of resins. The gold concentration after this stage is often of the order of 20 ppm. A further rinse is often effected with the gold concentrations being brought down to the order of 10 ppm, at which point it is assumed that no further gold can normally be economically recovered.
In the past, apparatus operating on the principles of electrolytic deposition, have been utilized in an effort to electrolyze the relatively dilute solutions as above, to hopefully recover in economic fashion, the gold or other metals remaining therein. One good example of such a device is said forth in U.S. Pat. No. 3,859,195, wherein apparatus for electrochemical processing is disclosed, utilizing a series of concentric extended extended-surface electrodes. In this device, treatment of the electrolyte is effected by passing same axially through a cylindrical container holding the concentric electrodes. The electrodes preferably comprise corrosion resistant metal filaments, which are fabricated into knitted form.
A further disclosure of interest for present purposes is the electrode structure set forth in U.S. Pat. No. 4,046,663. There a canister holds a plurality of side-by-side graphite fiber tows. The canister carries a series of openings on its lateral surfaces. The electrolyte is fed into the canister and is filtered through the carbon fibers and passes out through the openings in the canister walls. The electrolyte then proceeds through a concentric counter-electrode and then through a spaced outlet. The device functions much like a mechanical canister filter, although it is, of course, electrochemical in nature.
By and large, the prior art devices, while they have achieved a degree of success, have been incapable of effectively and rapidly removing the metals sought to be recovered from the relatively dilute electrolytes. Especially to be noted is that while many of the prior art devices have indeed been capable of recovering the sought after metals when the devices were operated for very sustained periods of time, economics dictate that not only must such a device be capable of removing metals from relatively dilute concentrations of same, but also the removal must be at a sufficiently rapid pace to render the device practical and useful.